Method for producing molded articles under heat and pressure



Dec. 19, 1939. v. H. TURKINGTQN -METHOD FOR PRODUCING MOLDED ARTICLESUNDER HEAT AND PRESSURE Original,I Filed May 14, 1934 ATTRNEY PatentedDec.; 19, 1939.

UNITED A STATES' LIETHOD FOB PRODUCING MOLDED ARTI- CLES UNDER HEATPRESSURE i Victor H. Turkingto to Bakelite Corporati n, Caldwell, N'QJ.,assigner on, New York, N, Y., a

corporation or Delaware substitute mi applications sean. No. 125,515125,511, and 125,518, my 14,1934. 'rms n p11-camu.. october. zz, 195s.semi Na. saam 1'! Claims. v(Ul. 18--55) This invention relate's to amethod and apparatus for the production of compositions comprising aiibrous` ller and a binder, that are molded or otherwise formed intomaterials or 5 directly into articles by means of the application ofheat and pressure, or heat and pressure with after-cooling underpressure, wherein high im-l pact strength and a minimum oi dimensionalchange under heat or in the presence oi' moisture L0 or oils or otheruids are of importance.

The invention includes compositions comprising a ller and athermoplasticV binder that are molded under a higher heat-pressure-lowerheat cycle as well as compositions comprising-a iiller l5 and a urearesin binder, that are molded under heat and pressure into semi-iinishedmaterials or directly into articles, and more particularly to materialsoi' a laminated character comprising a fibrous sheet or brous sheetsbonded to- :0 gether under.the heat-pressure-cooling cycle or under heatand pressure, which may be machined into various articles, for instancegears and the like wherein high impact strength and low speciilc gravityare of importance and a minimum :5 of swelling or dimensional change inthe presence oi moisture and oils are desirable.

Ordinary molding powders of apparent density of 0.1i to 0.6 are now incommercial practice often .subjected to two successive molding cycles :oin that they are ilrst preformed or pilled on a tablett'ing machineusing room temperatures and pressures of 8000 'to 10,000 lbs. per squareinch'. These pills are very weak mechanically since the powder hassimply been compressed to exclude :5 air and no great amount oi plasticow has occurred. They are weak due to a discontinuous state of thebonding agent but have a very desirable density range of about 0.8 to1.0 specific gravity. When such pills are molded under heat ,0 and-pressure they are compressed to a specic gravity about 1.35 to 1.4.

Commercial methods for molding under heat and pressure also consist ofimpregnating fabrics or mixing lling materials with bonding pow- 5 ders,molding under heat and pressure either under flat plates or in a shapedmold with at least one movable element, in order tocompact the heatedmass into a hard, dense structure. The urea resinoid materials underheat andpres# 0 sure become hard and may be removed hot from the mold.In urea. resinoid molding materials it is customary to leave a deiinitepercentage of combined water or other dissolved material which mayA actas ilowing agents or lubricants, remain- 5' ing in the nished productafter molding. The

y bonded by resins into an article oi' speciilc grav- `In doors, theexpansion'and contraction may to change by contact with water.v

thermoplastic materials now' under heat and pressure to form a densemass which retains this density when the article is cooled as it mustAbe for removal from the mold since the themaplasticsdo not solidifyunder heat. 5 Reacted or shaped materials made as above, arecharacterized by very dense structure. for instance wood having anapparent specific gravity of approximately 1.0 is ground into pulp andlo ity of 1.35 to 1,50 and mayy be fashioned into gears,lbuildlnselements for instance handles, wallboard, boxes, doors, andsimilar articles but they are nevertheless aiected to a suicient ex-.tent by swelling agents, for instance moisture and/or heat to result ina pronounced dimensional changev o! the whole mass. In wallboard, theexpansion .and contraction may result in a loose ntting board in dryweather and one which expands and warps in hot weather. For such usesfor instance in -automobile timing gears, where gear teethmust beaccurately cut and ntted, slight swelling results in binding and inexcessive wear in spots with consequent noise.

result in a loose fitting door in dry weather and one which sticks inwet weather. In the case of the urea materials molded into doors andsimilar articles, these may be colored as desired since the basic ureamaterials arev without color and stable to light. The urea resins incontact with for instance, phenoiic-aldehyde resins have been subject.to two denite commercial faults namely cracking with age and avpronounced sensitivity The present invention provides means and methodtogether with suitable materials for the production of shaped articleswhich are superior to thoseabove mentioned in comparative freedom fromswelling or change in dimensions under severe conditions of heat,moistureaor oil, or both swelling and change, and more economical byreason oi a lower speciilc gravity in the bondedv piece.

I have discovered that if the previously mentioned pills or moldingmaterial are saturated withl a volatile non-solvent they can beheattreated under pressure and become oi high strength with continuousbonded structure but with a vesiculated structure still having adesirable low gravity of less than 1.2. Articles made in accordance withthis invention are surprisingly superior to those obtained from bondedmaterials produced in theusual way and in common use, particularly intheiry mechanical l hitherto known compositions.

strength, low cost per unit volume, and freedom from expansion andcontraction, characteristics which are evidently highly desirable onaccount of economies of design that are possible with a than thestandard high density mlded plastics,

all of which renders the material particularly applicable for theproduction of fbuilding elements.

Briey stated the improved pressure molded articles made in accordancewith the present invention involving the expansion or vaporization underheat and pressureof a non-solvent iiuid correlated in expansion underheat to the softening and hardening temperatures of the plastic,

are obtained by a controlled means of directly producing in the bondingmedium small voids or poresresulting from the presence of discreteparticles of the non-solvent giving a honeycomb or spongelike structure;that is, the heat` and pressure bonded structure is vesiculated orformed as a network. I may use a non-binding material of uid producingtype to produce stronger structure of the binder such for instance, asthe use of ammonium carbonate, methyl malonic acid, or diazoacetamidein, for instance, a thermoplastic resin like polymerized styrene or atemporarily thermoplastic binder resin like the masses fromureaformaldehyde which harden under the action of heat. For

convenience I shall denominate the resulting physical structure of thebinder as porous including thereby those structures wherein the voids orpores of the bond are unfilled or are filled temporarily with some thirdingredient. Fillers may be used with the binders containing the poreproducing ingredient. Fillers include any solid@ except those solid poreproducing substances which occupy a much greater space when heated, forexample ammonium carbonate which decomposes when sufficiently heated.

A specific method of securing a porous structure comprises preparing acomposition by impregnating a woven fabric or a felted sheet with anappropriate plastic material and driving oil' the solvent by heat. Thethermoplastic materials are those binding materials which iiow underheat and pressure and require a lower temperature before discharge fromthe hot molding cycle. but which are not substantially changed 00 in themolding cycle and may be remolded as often as desired. The resinoids areresin compositions which may also contain fillers, rendered plastic forinstance by water but convertible to a hard, infusible, insolublecondition by heat.

05 Inithe case oi the urea aldehyde resinoids, this includes the ureaformaldehyde resinoids, the urea thio-urea aldehyde mixed 'resinoids,the ureaaldehyde resinoids generally and in general the V bindingmaterials derived from urea or sub-k v stituted ureas as well as thepotentially reactive phenol-formaldehyde resinoids and the phthalicanhydride-glycerol resinoids which may be set to a hardenedcondition/and rendered substantially infusible by heating. Theimpregnated` i sheet is then soaked in' adapproprlate liquid,

for instance water, gasoline, ethyl diazoacetate, etc., which is anon-'solvent for the finished binder and which is volatile at orbelowthe -highest heat used in the molding cycle or inthe case of thethermoplastic materials, which is a volatile at or below the meltingpoint of the plastic as measured under molding pressure used in themolding cycle until the sheet is penetrated to the desired amount, afterwhich it is cut and built up into packs or the packs can be made up fromimpregnated fabric and then soaked and nally subjected to heat andpressure, preferably in the manner hereinafter described. Theliquid-containing pieces may be used for the entire structure or anypart thereof, for instance in a gear the shock resistant material may beon the rim and the usual high density material near the hub. In abowling ball or handle, the porous light weight shock resistantnon-cracking material may be at the center and in wallboard the vporous, shock resistant material may be on the surface and the usualhigh density material at the center. The porosity, shock resistance,gravity, etc., may thus be controlled in any part of a molded article.

In following the customary pressing or molding procedure, some of theexcess non-solvent is forced out and an additional amount may be lost byevaporation. However, part of the expanded non-solvent remains whilek,the binder is reaching the stage where it is set and will no longer owunder applied pressure and is ready for discharge from the mold, thisnon-solvent occupying a portion of the total volume and being intimatelymixed with the binder and filler. During the latter stages of theheating period or in a subsequent heating after removal from the press,the evaporable non-solvent may be expelled leaving a vast number of veryminute pores in the material. It is usually desirable, however, to leavea certain amount of water in the materials containing cellulose filler,say, from 2% to 6% of the weight of the inished piece as this tends topreserve the strength of the cellu lose filling material.

The temperatures and pressures of the press should preferably becorrelated and the temperature in the case where the material is heatedafter removal from the press, should be regulated with the end in viewthat the non-solvent should form a vapor phase or a discrete portion ofthe structure in order to produce pores and hold these structural poresopen until the material has set, 'after which the non-solvent may beremoved or 'not as desired and subsequent heating either with or withoutpressure may be used to harden the material' to the extent desired.

It will be understoodthat considerable variation in the structure of thematerial can be produced by varying the amount of non-solvent used andalso by varying, in the molded article the proportion and/or position ofthe non-solvent treated material used and also by varying the conditionsof pressing, such as time, temperature and pressure in either theheating orcooling part of the cycle, or both, and their correlation. Inthe case of urea materials it is desirable to have free water or othernon-solvent present at the time the material is set under heat. Thecharacteristics of the molded piece may@ further be controlled by thevapor in which it is molded.

It will also be evident that water is not' the only ingredient suitablefor producing a porous structure containing voids as described above,and

4filler is impregnated, can be retained in whole or in part instead ofsubstituting water or other liquid and the pack or superposedlaminations built therefrom. It is usually found more satis' factory,however, to use such as are not solvents for the synthetic resinoid orbinding material.

Instead of soaking the binder impregnated fabric or other composition ofbonding agent and flller in water or other liquid, other means can beused for applying it; for instance, the composition can be placed in achamber where the humidity or vapor concentration of the nonsolvent maybe controlled to secure a definite amount of the liquid in the fabric;or the liquid caribe sprayed thereon. Another method is the use in thefabric impregnating step of a solution of the binder in a mixture ofsolvents containing a considerable amount of water or other ingredientand then controlling the drying operation so as to leave the desiredamount of water or other ingredient in the binder impregnated fabric.Still another way of obtaining the ma'- terial is .to form a dispersionof the resinous material or of the resinous material with nonliquidingredients as pigments, colors, etc., and blend the'iiller with this.Ihe resinous mate'- rial may be either the continuous or dispersed phasebut preferably the continuous phase.` The term "dispersion is intendedto include emulsions or other suspensions. The dispersions may beprepared by agitation of a liquid or liqueed resinous material withwater or other liquid or liquefied material in the absence or presenceof an emulsifying agent, for instance metallic soaps, Y

preferably emulsifying agents which are soluble in the resinousmaterials and substantially in-v soluble in the water or othernon-solvent which is to be the dispersed phase.

As still another modification, there can be vadded either to theresinoid ingredients or to the impregnating solution, a substancecapable of being partly or completely decomposed to a gas at the moldingtemperature, as for example a salt, such asammonium carbonate. which, asin the case of the ureas, remain substantially unaffected at thetemperature of softening of the resinoid ingredients. Y

Whatever the'means employed, tliefeature regarded as important for ,thepurposes of this invention as covered more specifically in the presentapplication is that the resinoid or the combination of the-resinoid bondand ller, at the beginning of the pressing and heating operation, shallcontain or engender a. third ingredient under such conditions correlatedto the third ingredient as to cause the third ingredient to occupy spaceuntilthe resinoid is set and, if necessary, capable of then being drivenout of i the material in any suitable manner, for instance,

canvas or cloth scrap, cotton flock,l wood-, iiour, asbestos or otherfilling materials.

Several illustrative examples of materials to which the invention isapplicable are the following:

As an example of thermoplastic synthetic composition suitable for thispurpose, 100 parts of taining fabric or other nllers,.such as Ychippedan oil soluble phenolic resin are made by reacting 1 mol .of tertiarybutyl phenol and 1 mol formaldehydein the presence of .l mol alkalinecatalyst to a hardwaterfree resinous state and blending with from 20 tov300 parts of fatty oils either drying or non-drying and heating untilthe total mass becomes a composition with permanently thermoplastic,non-heat-hardening resinous properties 'with melting points as desiredbetween C. and'200" C. Water is a, suitable non-solvent liquid at theproper pressure for producing low ,specific gravity material with thisthermoplastic bond and ammonium carbonate or acid carbonate are suitablenon-solvent solids.

Commercial synthetic resins as those of the Vinyl ester or ether type,for instance, composed of mixture of vinyl acetate and vinyl chloride,polymerized by heating in presence of .1 per cent of benaoyl peroxide toa melting point of between 70 C. and 200 C., may be used. Commercialhexane, gasoline, and V. M. and P. naphtha, etc. are suitablenonsolvents for use with this grou'p of products.

Polymerized styrene may be used, for instance, with liquids like water.i

Cellulose acetate, made for instance from cellulose and acetic anhydridemay 'be produced with melting points between '70 C. and 200 C. andmolded in the presence of such indierent solvents as methyl alcohol,gasoline, naphtha,

those previously described, are preferred.

The thermoplastic materials flow under heat and pressure but must bechilled in order to harden before discharge from the mold; they are notchemically changed'in the molding cycle and may be remolded.

As an example -of a thermosetting urea resinoid reacted with 130 partsof 371,% formaldehyde solution in the presence'oi 2 parts ofhexamethylenetetramine for 20minutes under reiiux. To the resultingsolution 2 parts of citric acid are 55'. suitable for this purpose 60parts of urea arev added together with 58 parts of alpha cellulosedesired color combination. This material which softens atapproximately90 C. is dried to constant weight at 60 C; and then usedwith water in the process herein described. In place-of urea, mixturesof urea and thiourea may be used. In place of formaldehyde otheraldhydes may be used in part. substituted ureas and substitutedformaldehydes can replace up to about threequarters of the totalmixture.

An illustrative apparatus for carrying out this invention is vshown inthe accompanying draw-` ing, wherein Fig. l shows a longitudinalvertice-i section of an apparatus particulirlfy adapted for Iand dyes,lubricants and pigments to form any articles having irregular surfacecontours.-

The press comprises a chamber l which is capable ,of withstanding thedesired pressure for instance a minimum of 150 lbs. per square inch.

'I'he chamber is fitted with valved pipe connections 2 and 3forproviding circulation and pressure control of a desired fluidmediumwhichmay be steam, hot oil, or any other gaseous or liquid hot orcold material which may best be suited to the various modifications ofthe desired process, for instance that outlined above. Theresin-impregnated pack d is placed inside the chamber betweenspacingplates 5, or steel molds may be lled with the material and assembled ina stack where it is desiredto produce molded shapes other than datsheets. Stainless steel or chromium surfaced molds are preferred toprevent staining of the molds and sticking of the molded material.Controlled 'mechanical pre..- sure is applied, for instance, through aram operating in a hydraulic cylinder l. A piston ring 8 is used to sealthe pressure chamber, or a gasket may be substituted to bev squeezedagainst the walls to make a tight joint. Other means may be used to sealthe chamber, such as an ordinary stuilng box. 4 t

This type of apparatus has the advantage that whatever volatileingredient is included in the plastic mixture for producing the porousstructure as described above, it may be retained in the material in thedesired quantity and for the desired length of time and there is notendency for the center of the piece to differ in composition orstructure from the outer portions. The heat is quickly and uniformlytransmitted to the whole mass of material and the surrounding uid-medium exerts a hydrostatlilzpressure which may be high enough to givea olding pressure over the portion of the plastic material which is notsubjected to the direct pressure of the ram or 'for a heatedfluid can becirculated in the chamber I, if necessary, to supply the heat requiredwhich is readily transmitted through the spacing plates or`molds. Thesame is true for a cooling `fluid which is desirable for cooling theVmolded mass where a thermoplastic material is used.

' By varying the amount or type of vapor, for

instance water, carried by another vapor or'gas.- for instance air, vitis possible to control the amount of non-solvent in the plasticmaterial; for instance'where saturated air is used very little moisturewill be removed from the plastic material and, in fact, moisture may beadded to tain porosity at the center, the porosity of the exteriorportions may `be increased or decreased by increasing or decreasing the-amount of nonsolvent vapor surrounding the molded piece and thuscontrolling the loss of non-solvent from the surface of the piece beingmolded. 'I'he time, temperature and pressure of molding may becontrolled so that the eiect of the vapor extends inwardly from thesurface to the' desired depth.

Furthermore, a vacuum may be applied to this chamber to assist informing or holding the porous structure during the heating or coolingmolding cycle or both. As previously stated, the surrounding iiuidmedium which enters the chamber through the pipes 2 and 3 may be hot orcold water or oil as well as steam. For thermoplastic materials whichsoften at a low temperature, a vapor may be applied under a partialvacuum or hot or cold air either dry or carrying the desired amount ofmoisture or other vapor may be used. In this way, either a thermoplasticmateplication of vacuum` will assist in cooling thely plastic mass byvaporization of the low volatile y liquid.

The fluid chamber type of press is also excepy tionally well adapted tomolding single very large with a minimum of internal strain and amini--l mum-of cracking since the-chamber iiuid pro- 1 vides means forapplying heat more directly,

simultaneously, and uniformly with greater efficiency to all parts ofthe piece than where heated platens or indirect heating means are used,thus minimizing strains in the molded piece.

For" convenience in loading and unloading, the chamber may be arrangedso that it can be swung or moved to one side allowing free access to thetop. A loading rack 9 can be provided so that the entire charge may beassembled and lowered into the chamber at one time by handholdsremovably threaded into the openings I8 or in any other suitable manner.

Means for heating and for cooling the walls of the chamber and theplunger may take the form of spaces II for the heating or cooling medium which may enter or exit through the valved pipes I2. These may beused to control the circulation and pressure of the'medium and thuscontrol temperature. In case only heating is desired, electrical heatingelements may be in the spaces I I-with leads passing through the pipesI2.

I n Fig. 2 is shown molding means I3 for producing pieces Il having anirregular contour.

These pieces may, for instance, be gears or doors molded nearly orlentirely to nished size. I prefer. to shapel a number Iof thesearticles in one operation-and therefore use a series of cooperating dieshaving mold lshapes on both faces so that they may-be stacked withintermediate layers of molding material. Thus, when pressure is appliedto the top die, a number of articles 'are produced in one operation ofthe press. If it is desired to produce shaped articles which have aperimeter nearly or entirely of the desired size, I may and prefer touse sidsupports I5 which act as retaining walls for the Y shaped piecesand 35 and/or thick pieces for instance heavy doors, v

guides for the freely moving-die parts. The supports I may be providedwith openings to permit steam to contact with the molding material andenter the openings through the dies I3. d 5 Materials made in accordancewith this'invention and characterized by a porous structure have anunusually high resistance t'o impact as compared to the high densityproducts; and although 'they are not impervious. to water and mayactually absorb greater percentages of water by Weight than present highdensity commercial materials, they do not swell as much in over alldimensions and do not warp or crack whenA exposed for long periods oftime to either hot or cold water or moisture or oils. This property Amakes them especially adapted for mechanical uses and for articles whichare frequently or continuously in contact with water or moisture oroils, such as handles, washing machine agitators, wallboard, molded heatinsulation, molded gaskets, etc., as Well as gears, doors and similararticles. If desired, the materials may be given a surface coating ofwater or oil resisting material to prevent the transfer of water and theconsequent lling of the pores'of the material.

A further advantage is that materials made in accordance with thepresent invention are lighter in Weight due to the porosity of theresulting structure and therefore eiect savings in the amount" requiredto produce an article of any given size or volume. This saving in somecases amounts to 20% Aor more as compared with articles formed inaccordance with the practice of the hitherto known art. The lightness in`weight and the freedom from dimensional change, aside from the savingin material, is also advantageous for many articles as for instancetable tops/and other pieces of furniture. etc. where a strong,

light weight, light colored material adapted to coloring and exactstaining to simulate wood or give other desirable eilects-is ofdenitecommercial value. Whereas present molded vmate-- rials made from cottonduck and plastic resins such' as the urea formaldehyde` resins have aspecific gravity of 1.46 to 1.40, the materials made from the sameingredients and processed in accordance with this invention have a muchlower specific gravity ranging from 1.25 to 1.00

or less than 1.00. Where other types of resinous materials and fillersare used, the speciic gravities, of course, will be'diierent from theabove figures but, in general, the specific gravity of any resinousmixture treated in `accordance with this invention will becorrespondingly lowand will be -less than it would be ii treated inaccordance with the prior art methods. t

The present application is a continuation of my co-pending applicationsSerial Numbers 1. Method of molding plastic materials under heat andpressure which comprises forming a material which can be renderedplastic by heat and then hardened, incorporating with said material anadded'ingredient which expandsat the temperature at which the materialbecomes plastic to thereby produce pores in the plastic material,molding the mixtureunder such heat and pressure as to expand the addedingredient while the mixture is plastic to'produce pores and surroundingthe plastic mixture while being molded with a medium capable of,minimizing the dissii pation of the ingredient from the material, and

hardening the material.

2.'Metho`d of moldinggplastic materials underv the material while holdthe porous structure.

725,576, 725,577, and 725,578, led May 14, 1934. l

heat and pressure which comprises forming a f material which canA berendered plastic by heat and then hardened, incorporating water withsaid material, moldingthe mixture under such heat t and pressure as tovaporize the water while the 5 mixture is plastic to producepores andsurrounding the plastic mixture while being molded with steam capable ofminimizing the dissipationv of the water from the material, andhardening the material. Y

3. Method of producing plastic materials under heat and pressure whichcomprises forming a material which can be rendered plastic by lheat andthen hardened, incorporating with said material an added'ingredientwhich expands under 15 heat during a later stage of the process, theexpansion temperature of the added ingredient being correlated to theplasticizing and hardening temperatures ofsaidmterial so that the' addedingredient expands within the plastic material to produce pores, moldingthe mixture under such heat and pressure as to expand the addedingredient while the mixture is plastic to produce pores and surroundinglthe plastic mixture while being molded with a medium cag5 pable ofminimizing the dissipation of the said ingredient from said material,and hardening the material.

4. A process of producing porous articles from l a thermoplasticmaterial, which comprises pro-Il 30 viding a thermoplastic materialwhich'softens under heat and hardens when cooled, incorpo-- rating with.said material a liquid ingredient which expands during a later stage ofthe process, expanding the liquid and molding the mixture 35 under heatand pressure whereby pores are produced and performing the molding stepin a closed chamber with the plastic mass surrounded by fluid 'tominimize dissipation of the liquid from the mass during molding, andhardening 40 in theporous condition to 5. -A process of producing porousarticles from a thermoplastic material, which comprises providing athermoplastic material which softens 45 under heat and hardens whencooled, incorporating with said material a liquid ingredient whichexpands during a later stage of the process, expanding the liquid andmolding the mixture under heat and pressure whereby pores are pro- 50'-to hold the porous structure.

6. A processlof producing porous articles comprising a thermoplasticmaterial, which comprises providing a thermoplastic material whichsoftens a@ under heat and hardens when cooled, incorporating with saidmaterial a liquid ingredient which expands during a later stage of theprocess, expanding the liquid and molding' the mixture under heat andpressure whereby pores are pro- 65 duced and performing the molding stepin a closed chamber with the plastic mass surrounded by an atmospherecomprising the said liquid to minimize dissipationof the liquid from themass during molding and hardening the material while 70 in the porouscondition to hold the porous structure.

7. A process ofi produc g porous articles from a synthetic.thermoplastimmateriaL which comprises providinga'thermoplastlc\material which 75 8. A process of producing porousarticles from a thermoplastic material, which comprises providing athermoplastic material which softens under heat and hardens when cooled,incorporating with said material a vaporiaable ingredient which expandsduring' a later stage of the process, expanding said ingredient andmolding the mixture under heat and pressure whereby pores are producedand perfo the molding step in a closed chamber with the plastic masssurrounded by a medium of controlled characteristics to control theamount of said ingredient crossing the surface or the mass duringmolding, and hardening the material while in the porous condition tohold the porous structure.

9. A` process of producing porous articles comprising a thermoplasticmaterial which comprises providing a thermoplastic material whichsoftens .under heat and hardens when cooled, incorporating with saidmaterial an.- added ingredient which expands during a later stage in theprocess, expanding the added ingredient and molding the mixture underheat and pressure whereby .pores are producedand hardening the materialwhile in .the porous condition to hold the porous structure and perfthestepoi,

hardening the mixture under alvacuum to assist in holding the porousstructure.,

l0. A process of producing porous articles comprising athermoplasticmaterial which comprises providing a thermoplastic materialwhich softens under heat land hardens when cooled, incorporating. withsaid material an added ingredient which expands during a later stage inthe process, expanding the added ingredient and molding the mixtureunderheat and pressure whereby pores areproduced and hardening the materialwhile in the porous condition -to hold the porous stmo- .ture andperforming the step of molding the mixture under a .vacuum toassistinforming the being molded with an atmosphere capable ofporouastructure.

1l.. A process of producing porous articles comprising a thermoplasticmaterial which com- 'prisesproviding a thermoplastic material whichsoftens under heat and harden's when cooled, incorporatingwith saidmateriall an added ingredient which expands during a later stage in theprocess, expanding the added ingredient fand 4molding the mixture underheat and pressure whereby pores are produced and hardening thematerial'while in the porous condition to hold the porous structure and`performing the step of expanding the added ingredient while themixtureis-under a vacuum to assist in forming the porous structure.

12. -A process oi producing porous articlescomprisingl aH urea-aldehyderesinoid, which. comprises iorming a urea-aldehyde resinoid capable ofhardeningun'der heat and pressuraincorpo-n rating with said vresinoid aliquid ingredient whichexpands'dur'ing a'latel stage ot the process butwhich remains iree in the mixture, molding the mixture under such'h'e'atandpressure in a chamber oilarger dimensions the nished article as tovaporize the' liquid ingredient while the mixture is plastic to producepores and surrounding the plastic mixture while being molded in thechamber with a iluid capable o! minimizing the dissipation ofthe liquidfrom the mass during molding, and hardening the resinoid to retain theporous structure.

1.3. A process of producing porous articles comprising a urea-aldehyderesinoid which comprises forming a urea-aldehyde resinoid capable ofhardening under heat and pressure, incorporating with said resinoid aliquid ingredient which expands during a later stage oi the process butwhich remains freein the mixture, molding the mixture under such heatand pressure in a closed chamber of larger dimensions than the nishedarticle as. to expand the liquid ingredient While the mixture isplasticto produce pores and surrounding the plastic mixture while being moldedin the chamber with a uid under pressure capableoi` exerting an evenhydrostatic pressure upon the parts of the .plastic mass exposed to thefluid during molding, and hardening the resinoid to retain the porousstructure.

14. A process of producing porous articles comprising aurea-aldehyderesinoid, which comprises forming a urea-aldehyde resinoidcapable of hardening under heat and pressure, incorporating with saidresinoid a liquid ingredient which expands during a later stage of theprocess butwhich remains free in` the mixture, molding the mixture undersuch heat and pressure in a closed chamber of larger dimensions than theilnished article as to expand the liquidJ while the mixture is plasticto produce pores and surrounding-the plastic mixture while being moldedin the chamber with an atmosphere comprising said ingredient andcapableof minimizing the dissipationof the liquid from the mass during molding,and hardening the resinoid to retain the porous structure.

15. A process oi producing porous articles comprisinga urea-aldehyderesinoid, which comprises forming a urea-aldehyde resinoid capable ofhardening under heat and pressure, incorporating waterwith said resinoidin suicient amount to have free ywater in the mixture, molding themixture vunder such heat and pressure as to vaporize--the water whilethe mixture is plastic to produce pores, surrounding the mixture whilecontrolling the escape oiwater from the mixture, and hardening theresinoid to yproduce a hardened porous structure.

16, A-process 'of producing porous articles comprising a urea-aldehyderesinoid. which comprises,

providing a urea-aldehyderesinoid capable of hardening under heat andpressure, incorporatingwith said resinoid a vaporizable ingredient whichexpands during a later stage oi the process but which remains free inthe mixture, molding -ftheinixture undersuch'heat and pressure in aclosed chamber of larger 'dimensions than the nnished article'as t'oexpand the ingredient while the mixture is plastic to yproduce pores andsurrounding the plastic mixture while being molded masias? 4 l 7 forminge urea-aldehyde -resinoid capable ot hardening under heat and pressure,incorporating with said resinoid a volatile ingredientwhich expandsduring a. later 'stage of the process,

v molding lthe mixture under such hem;l and pressure in a closedchamberos to dvolaizilize the said ingredient while the mixture isplastic to.

produce pores and surrounding the plastic mix? ture while being moldedin the chamber with uid at a subs-atmospheric pressure to'as'sist linholding the pores, and hardening th resinoid to retain the porousstructure.

y vI'c'roR H. TURxmGmN.

